Re: POC, WIP: OR-clause support for indexes

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From: Alena Rybakina <[email protected]>
To: Alexander Korotkov <[email protected]>
Cc: Ranier Vilela <[email protected]>
Cc: Alexander Lakhin <[email protected]>
Cc: jian he <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Nikolay Shaplov <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Peter Geoghegan <[email protected]>
Cc: Marcos Pegoraro <[email protected]>
Cc: [email protected]
Cc: Peter Eisentraut <[email protected]>
Cc: Andrei Lepikhov <[email protected]>
Subject: Re: POC, WIP: OR-clause support for indexes
Date: Fri, 31 Jan 2025 17:31:44 +0300
Message-ID: <[email protected]> (raw)
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Hi!

On 25.01.2025 08:04, Alexander Korotkov wrote:
> On Wed, Jan 15, 2025 at 10:24 AM Andrei Lepikhov<[email protected]>  wrote:
>> On 1/13/25 10:39, Andrei Lepikhov wrote:
>>> On 1/13/25 01:39, Alexander Korotkov wrote:
>>> It can be resolved with a single-line change (see attached). But I need
>>> some time to ponder over the changing behaviour when a clause may match
>>> an index and be in joinorclauses.
>> In addition, let me raise a couple of issues:
>> 1. As Robert has said before, it may interfere with some short-circuit
>> optimisations like below:
>>
>> EXPLAIN (COSTS OFF)
>> SELECT * FROM bitmap_split_or t1
>> WHERE t1.a=2 AND (t1.b=2 OR t1.b = (
>>     SELECT sum(c1.reltuples) FROM pg_class c1, pg_class c2
>>     WHERE c1.relpages=c2.relpages AND c1.relpages = t1.a));
>>
>> Here, a user may avoid evaluating the subplan at all if t1.b=2 all the
>> time when t1.a=2. OR->ANY may accidentally shift this behaviour.
>>
>> 2. The query:
>>
>> EXPLAIN (ANALYZE, COSTS OFF)
>> SELECT * FROM bitmap_split_or t1
>> WHERE t1.a=2 OR t1.a = (
>>     SELECT sum(c1.reltuples) FROM pg_class c1, pg_class c2
>>     WHERE c1.relpages=c2.relpages AND c1.relpages = t1.a)::integer;
>>
>> causes SEGFAULT during index keys evaluation. I haven't dived into it
>> yet, but it seems quite a typical misstep and is not difficult to fix.
> Segfault appears to be caused by a typo.  Patch used parent rinfo
> instead of child rinfo.  Fixed in the attached patch.
>
> It appears that your first query also changed a plan after fixing
> this.  Could you, please, provide another example of a regression for
> short-circuit optimization, which is related to this patch?
>
> Also, I've integrated your fix from [1].
>
> Links.
> 1.https://www.postgresql.org/message-id/41ba3d47-2a48-476c-88d4-6ebd889a7af2%40gmail.com

I started reviewing at the patch and saw some output "ERROR" in the 
output of the test and is it okay here?

SELECT * FROM tenk1 t1
WHERE t1.thousand= 42OR t1.thousand= (SELECT t2.tenthousFROM tenk1 t2 
WHERE t2.thousand= t1.tenthous);
ERROR: more than one row returned by a subquery used as an expression

-- 
Regards,
Alena Rybakina
Postgres Professional

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